So far, for example, Patent Document 1 discloses a fuel injection system for an internal combustion engine. A fuel injection valve in this conventional system incorporates a heater for heating fuel immediately before being injected. This heater is configured to produce heat by receiving a supply of electric power from a predetermined electric power source. In the aforementioned fuel injection valve, the resistance value of the heater is set to a value within a predetermined range so that the surface temperature of the heater falls within a predetermined temperature range in which a deposit does not adhere.
The temperature of the heater can be estimated on the basis of an unambiguous relationship with the resistance value of the heater. In addition, the resistance value of the heater can be calculated on the basis of electric voltage that is applied to the heater (voltage between both ends of the heater) and electric current that flows through the heater. However, an error may be produced in the estimated temperature value of the heater due to factors of variations concerning its hardware (for example, a variation in the resistance value of the heater, and a variation in the resistance value of a wire harness that supplies the heater with electric power).